Agrobacterium tumefaciens is a common soil bacterium that causes crown gall
disease on many dicotyledonous plant species. It has been exploited for use in genetic
engineering because it is able to promote transfer of any DNA segment to plant
chromosomes. Many molecular factors in both the plant and bacterium contribute to
successful infection and DNA transfer.
Two bacterial factors were studied for this dissertation. The first was bacterial
synthesis of cytokinins due to the induced expression of the gene tzs. Cytokinin
production by some A. tumefaciens strains at the time of infection was hypothesized to
enhance infection or influence host range. To test this hypothesis, heterologous strains
engineered to express tzs and a native strain from which tzs was deleted were evaluated
for tumor induction on a number of plant species. Major differences were seen when
radish roots were infected with the tzs deletion strain. Morphological differences of the
galls formed suggested a possible role for tzs in T-DNA transfer efficiency. β-glucuronidase
assays with a mannopine synthase promoter-uidA fusion gene were
used to study T-DNA transfer early in the infection process. No biological role for tzs
was confirmed with either tumorigenesis or T-DNA transfer assays. However, optimized
conditions for GUS fluorometric assays were established and the infection process was
characterized.
The second factor studied was a β-glucosidase gene in A. tumefaciens strain
83/73. This strain is highly infective on conifer hosts, whereas others are not. It is also
able to hydrolyze the conifer phenolic compound, coniferin, to an active virulence gene
inducer, coniferyl alcohol. This appears to be a major host range determining factor.
As a first step in proving this role, the gene for the β-glucosidase enzyme responsible
for hydrolysis of coniferin in strain B3/73 was cloned and sequenced. The deduced
protein sequence has homology to other β-glucosidases, including a conserved active
site. / Graduation date: 1991
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/37381 |
| Date | 08 August 1990 |
| Creators | Castle, Linda A. |
| Contributors | Morris, Roy O. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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